Hydrocarbon fluids such as oil and natural gas are obtained from a subterranean geologic formation, referred to as a reservoir, by drilling a well that penetrates the hydrocarbon-bearing formation. In some applications, the hydrocarbon-bearing formation is fractured and the features of the hydraulic fractures may be characterized via hydraulic fracture monitoring. In some applications, hydraulic fracture monitoring is performed with an array of geophones used to map micro seismic events occurring in the reservoir rock during creation of fractures. However, the acoustic energy created by the rock when fractured is sometimes too small to detect or the acoustic energy is generated by adjacent portions of the rock rather than the fracture itself. As a result, inaccurate data may be generated.